NLGN4X GENE OVEREXPRESSION IS ASSOCIATED WITH AUTISM AND PROFOUND MENTAL RETARDATION

Background: Truncating mutations in the X-linked Neuroligin 4 gene (NLGN4X) have been previously identified in few families with autism, Asperger syndrome and/or mental retardation (MR), suggesting that defects in its coding sequence are quite rare in these disorders. However, it could be conceivable that altered expression levels of the NLGN4X gene are present in autistic patients and associated with variations in regulatory sequences.

Objectives: To further investigate the role of NLGN4X gene in autism spectrum disorders (ASDs), we have explored its transcript level in individuals diagnosed with ASDs with a normal NLGN4X gene coding sequence.

Methods: We studied 96 unrelated French patients who met DSM-IV criteria for autism. Genetic disorders have been excluded by clinics and cytogenetics. Patients with FRAXA mutation were also excluded. The NLGN4X transcript level has been analyzed by quantitative RT-PCR using cDNA generated from lymphoblastoid cell lines (LCLs) from affected individuals.

Results: Using real time RT-PCR conditions, we identified a 3-fold increase in the NLGN4X transcript level compared to controls in one boy with autism and profound MR. This increased NLGN4X expression is associated with a de novo 1 bp (-335G>A) substitution which is located in the promoter region and not found in 450 normal X chromosomes. Moreover, this substitution is associated with the formation of one perfect ZID (Zinc-finger protein with Interaction Domain) binding site.

Conclusions: We report here the first description of an increased level of the NLGN4X transcript in LCLs from one patient with autism and profound MR. This result brings a new insight regarding the phenotypic spectrum of NLGN4X mutations, and suggests that the analysis of transcription level as well as regulatory sequences in this gene may reveal more individuals with mutations.